| AVS 61st International Symposium & Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF+PS-ThM |
| Session: | Advanced CVD and Chemical Vapor Infiltration Methods |
| Presenter: | Henrik Pedersen, Linköping University, Sweden |
| Authors: | M. Imam, Linköping University, Sweden C. Höglund, European Spallation Source (ESS AB) J. Birch, Linköping University, Sweden H. Pedersen, Linköping University, Sweden |
| Correspondent: | Click to Email |
The world-wide shortage of the 3He isotope has led to a need for novel designs of neutron detectors. A detector based on the isotope 10B, in the form of thin films, has been suggested by the European Spallation Source (ESS). The detector design uses 10B4C films, ≥1 µm, deposited on both sides of neutron transparent substrates such as Al blades.[1] The melting point of Al (660 °C) sets a strict upper temperature limit for CVD of the 10B4C films. Also, metallic Al will be badly affected by corrosive by-products, like HCl. This means that traditional B4C CVD routes based on BCl3 and CH4 cannot be used. An alternative CVD route is to use oragnoboranes, i.e. molecules with direct B-C bonds, as such molecules are very reactive and do not produce corrosive by-products.
We have demonstrated the synthesis of thin, X-ray amorphous, boron-carbon films at low temperature (400-600 °C), by thermally activated CVD using triethylboron, B(C2H5)3, (TEB) as single precursor on both single crystalline Si (100) and Al substrates.[2] Films with B/C-ratio of 4.6 with density 2.42 g/cm3 (bulk B4C density 2.52 g/cm3) and 3.6 with density 2.14 g/cm3 were deposited at 600 °C in hydrogen and argon ambient respectively, the impurity levels in the films was about 4 at.% of H at 600 °C. Further studies of TEB as precursor at higher temperatures (700-1200 oC) on Si substrates show that films with a B/C ratio of 4.5 and 3 were obtained from films deposited at 700 oC in hydrogen and argon ambient respectively with < 0.24 at.% of H. A threshold temperature of 1000 °C for the deposition is identified above which the B content decreases dramatically. Based on our results, a chemical mechanism for boron-carbon films from TEB, where the TEB molecule is decomposed to BH3 and hydrocarbons, is suggested.
Plasma Enhanced CVD using trimethylboron, B(CH3)3, (TMB) is also explored to further lower the deposition temperature. Results from CVD and PECVD will be compared with state of the art PVD of 10B4C.
[1] R. Hall-Wilton et al. IEEE NSS/MIC conference record, 4283 (2012)
[2] H. Pedersen et al. Chem. Vapor Deposition 18, 221-224 (2012)